Navigating Precise Deuteration via Vibronic Mode Analysis to Effectively Suppress Nonradiative Decay in Organic Donor–Acceptor Emitters

Deuteration effectively modulates excited-state dynamics in organic optoelectronic materials with precise deuteration preferred over perdeuteration. In this work, we performed vibronic mode analysis to explore site-selective deuteration effects on organic donor−π–acceptor (D-π-A) emitters. Computations revealed that the dominant vibronic coupling sites of tBTAP are primarily located at the π-bridge and then acceptor. Precise deuteration at these sites amplifies the total Huang–Rhys factor (∑ S j ) without significantly altering the reorganization energy, thereby suppressing the nonradiative decay rate ( k nr ) and enhancing the photoluminescence quantum yield (PLQY). As a proof of concept, tBTd-APd 1–2 with a deuterated π-bridge and acceptor halves k nr from that of tBTAP (1.81 × 10 7 s –1 ) to 0.93 × 10 7 s –1, achieving a PLQY (95.1% at 682 nm) higher than that of tBTAP (91.7% at 687 nm) in toluene. Observed trends in k nr suppression and PLQY enhancement are consistent across calculations, solution, and solid films. A nondoped near-infrared (NIR) OLED based on tBTd-APd 1–2 achieved a maximum external quantum efficiency (EQE max ) of 1.30% at 868 nm, one of the best results among reported NIR TADFOLEDs with emission peaks over 850 nm. This study navigates precise deuteration through vibronic mode analysis and highlights ∑ S j as a predictive metric to suppress k nr and enhance PL and electroluminescence performance for organic D-π-A emitters.